An automotive clutch generally comprises two coaxial clutch parts, one of which has at least one annular friction disc, i.e. a single friction disc or a plurality of friction discs axially spaced from each other, the other clutch part including a pressure plate which acts as a coupling member to couple the two clutch parts together when the clutch is engaged, and the other clutch part also including a reaction plate, for axial gripping engagement of the friction disc or discs between the plates. The pressure plate is under the control of a control means adapted to urge it in a direction towards or away from the reaction plate.
One of the clutch parts is coupled with a driving shaft for rotation therewith, while the other clutch part is coupled with a driven shaft, also for rotation therewith. The axial coupling of the friction disc or discs, when the clutch is engaged, brings the two clutch parts together in common rotation.
The control means may be of a hydraulic type, for example as described in the published patent document No. 1,600,183 of the Federal Republic of Germany. That document describes a control means in which the clutch includes two members cooperating with each other, one being a cylinder member and the other a piston member, these two members together defining a variable volume pressure chamber, with one of these members being movable with respect to the other. This movable member of the piston and cylinder assembly acts as the pressure plate of the clutch.
In another arrangement, the control means may comprise axially acting resilient means such as a diaphragm. Such an arrangement is described in French published patent application No. 2,616,501, in which the diaphragm is arranged to act in combination with monitoring means sensitive to the torque transmitted by the clutch, and with actuating means arranged to act on a declutching member in response to signals from the monitoring means. The declutching member is arranged to move the resilient means in such a way as to modify the coupling pressure on the pressure plate. In such a clutch, the transmitted torque depends on the control pressure exerted by the pressure plate and on the friction involved, in particular the coefficient of friction of the friction disc or discs and that obtaining within the clutch generally, this being influenced by the sliding action of the friction disc or discs.
In addition, the coefficient of friction is itself variable, especially as a function of speed. It is also influenced by the lubricating fluid when the disc or discs are lubricated by a fluid as described in the above mentioned West German patent document No. 1,600,183.
That document also discloses a torque limiter, of a kind comprising two parts defining a gap by which the two parts are spaced from each other. The two parts of the torque limiter are connected with each other through spacing means, the spacing between the two parts being variable as a function of torque. The torque limiter is coupled with the driving shaft for rotation therewith, and acts on the piston and cylinder assembly through an intermediate member so as to modify the pressure in the control chamber.
However, in order to avoid having to provide this intermediate member, it is possible to arrange the torque limiter so that it acts directly on the piston member of the clutch. Such an arrangement is described in U.S. Pat. No. 3,511,349.
In the above mentioned prior art documents, an object of the arrangements described is to limit the torque to a range of values about a predetermined datum value, without seeking modulation of the control pressure as a function of the requirement of the driven shaft. In addition, in all of this prior art, the torque limiter, where provided, is integrated with the clutch, being disposed within the space delimited between the reaction plate and the pressure plate. This makes it necessary to modify the general construction of the clutch itself.